Semiconductor switching modules are employed when the situation involves switching load currents of up to several hundred amperes frequently and virtually noiselessly, at operating voltages of a few hundred volts.
In this case, semiconductor switching modules can be produced for example according to so-called bonding technology. In this case, the actual power semiconductor element, comprising a base substrate and the power semiconductor chip fitted thereon and also further components, is connected to terminal elements by means of corresponding bonding wires. The terminal elements are routed outward through the module housing of the semiconductor switching module, such that corresponding interconnection with the load circuit to be switched can be performed. For electrical insulation both of the components and of the bonding wires, a large part of the interior space of the module housing is filled with an insulating potting composition. For heat dissipation purposes, moreover, an appropriately dimensioned heat sink is fitted on that side of the base substrate which is opposite to the side with the power semiconductor chip.
As an alternative, the power semiconductor element of such a semiconductor switching module can also be constructed according to so-called planar technology. Such a planar construction of a power semiconductor element is known from WO 03/030247, for example. In this reference, the components are fitted on the base substrate comprising a ceramic base with copper layers applied on both sides. The components can then be contact-connected to one another or be connected to terminal elements areally and without additional wires by way of further layers composed of electrically insulating and electrically conductive materials that are applied to the surface. The wirings required in bonding technology, and indeed those required in conventional soldering technology, are largely obviated through the use of such power semiconductor elements embodied in planar technology.
In addition, the insulation between the individual components and the electrically conductive layers is brought about here solely by the electrically insulating layers, such that an additional potting composition can be dispensed with. The electrically insulating layers thus serve, particularly when they extend virtually over the entire surface of the power semiconductor element, for increasing the creepage paths between the various conductive layers and components. Consequently, semiconductor switching modules can be produced more compactly, with less complexity and hence also more cost-effectively.
Power semiconductor chips in semiconductor switching modules, for example in the form of thyristors, have a control terminal for switching the load currents, a control signal being applied to said control terminal. Depending on the control signal, a load current passed via a load terminal and a base of the power semiconductor chip is then controlled and thus switched. In this case, the load circuit and the control signal can be connected by way of the bonding or planar technology described above.
Connection by way of bonding technology has the disadvantage, however, that it is very complicated. Connection exclusively by way of planar technology has the disadvantage that the planar electrically conductive layers for connecting the load and control terminals cover parts of the surface of the power semiconductor element and complex and complicated planar structures thus arise.